Compliant cardiac support device

ABSTRACT

A jacket of biological compatible material has an internal volume dimensioned for an apex of the heart to be inserted into the volume and for the jacket to be slipped over the heart. The jacket has a longitudinal dimension between upper and lower ends sufficient for the jacket to surround a lower portion of the heart with the jacket surrounding a valvular annulus of the heart and further surrounding the lower portion to cover at least the ventricular lower extremities of the heart. The jacket is adapted to be secured to the heart with the jacket surrounding at least the valvular annulus and the ventricular lower extremities. The jacket is adjustable on the heart to snugly conform to an external geometry of the heart and assume a maximum adjusted volume for the jacket to constrain circumferential expansion of the heart beyond the maximum adjusted volume during diastole and to permit unimpeded contraction of the heart during systole.

FIELD OF THE INVENTION

The present invention pertains to a device and method for treating heartdisease. More particularly, the present invention is directed to amethod and device for treating congestive heart disease and relatedvalvular dysfunction.

BACKGROUND OF THE INVENTION

Congestive heart disease is a progressive and debilitating illness. Thedisease is characterized by a progressive enlargement of the heart.

As the heart enlarges, the heart is performing an increasing amount ofwork in order to pump blood each heart beat. In time, the heart becomesso enlarged the heart cannot adequately supply blood. An afflictedpatient is fatigued, unable to perform even simple exerting tasks andexperiences pain and discomfort. Further, as the heart enlarges, theinternal heart valves cannot adequately close. This impairs the functionof the valves and further reduces the heart's ability to supply blood.

Causes of congestive heart disease are not fully known. In certaininstances, congestive heart disease may result from viral infections. Insuch cases, the heart may enlarge to such an extent that the adverseconsequences of heart enlargement continue after the viral infection haspassed and the disease continues its progressively debilitating course.

Patients suffering from congestive heart disease are commonly groupedinto four classes (i.e., Classes I, II, III and IV). In the early stages(e.g., Classes I and II), drug therapy is the commonly proscribedtreatment. Drug therapy treats the symptoms of the disease and may slowthe progression of the disease. Importantly, there is no cure forcongestive heart disease. Even with drug therapy, the disease willprogress. Further, the drugs may have adverse side effects.

Presently, the only permanent treatment for congestive heart disease isheart transplant. To qualify, a patient must be in the later stage ofthe disease (e.g., Classes III and IV with Class IV patients givenpriority for transplant). Such patients are extremely sick individuals.Class III patients have marked physical activity limitations and ClassIV patients are symptomatic even at rest.

Due to the absence of effective intermediate treatment between drugtherapy and heart transplant, Class III and IV patients will havesuffered terribly before qualifying for heart transplant. Further, aftersuch suffering, the available treatment is unsatisfactory. Hearttransplant procedures are very risky, extremely invasive and expensiveand only shortly extend a patient's life. For example, prior totransplant, a Class IV patient may have a life expectancy of 6 months toone-year. Heart transplant may improve the expectancy to about fiveyears.

Unfortunately, not enough hearts are available for transplant to meetthe needs of congestive heart disease patients. In the United States, inexcess of 35,000 transplant candidates compete for only about 2,000transplants per year. A transplant waiting list is about 8-12 monthslong on average and frequently a patient may have to wait about 1-2years for a donor heart. While the availability of donor hearts hashistorically increased, the rate of increase is slowing dramatically.Even if the risks and expense of heart transplant could be tolerated,this treatment option is becoming increasingly unavailable. Further,many patients do not qualify for heart transplant for failure to meetany one of a number of qualifying criteria.

Congestive heart failure has an enormous societal impact. In the UnitedStates alone, about five million people suffer from the disease (ClassesI through IV combined). Alarmingly, congestive heart failure is one ofthe most rapidly accelerating diseases (about 400,000 new patients inthe United States each year). Economic costs of the disease have beenestimated at $38 billion annually.

Not surprising, substantial effort has been made to find alternativetreatments for congestive heart disease. Recently, a new surgicalprocedure has been developed. Referred to as the Batista procedure, thesurgical technique includes dissecting and removing portions of theheart in order to reduce heart volume. This is a radical, new andexperimental procedure subject to substantial controversy. Furthermore,the procedure is highly invasive, risky and expensive and commonlyincludes other expensive procedures (such as a concurrent heart valvereplacement). Also, the treatment is limited to Class IV patients and,accordingly, provides no hope to patients facing ineffective drugtreatment prior to Class IV. Finally, if the procedure fails, emergencyheart transplant is the only available option.

Clearly, there is a need for alternative treatments applicable to bothearly and later stages of the disease to either stop the progressivenature of the disease or more drastically slow the progressive nature ofcongestive heart disease. Unfortunately, currently developed options areexperimental, costly and problematic.

Cardiomyoplasty is a recently developed treatment for earlier stagecongestive heart disease (e.g., as early as Class III dilatedcardiomyopathy). In this procedure, the latissimus dorsi muscle (takenfrom the patient's shoulder) is wrapped around the heart and chronicallypaced synchronously with ventricular systole. Pacing of the muscleresults in muscle contraction to assist the contraction of the heartduring systole.

While cardiomyoplasty has resulted in symptomatic improvement, thenature of the improvement is not understood. For example, one study hassuggested the benefits of cardiomyoplasty are derived less from activesystolic assist than from remodeling, perhaps because of an externalelastic constraint. The study suggests an elastic constraint (i.e., anon-stimulated muscle wrap or an artificial elastic sock placed aroundthe heart) could provide similar benefits. Kass et al., ReverseRemodeling From Cardiomyoplasty In Human Heart Failure: ExternalConstraint Versus Active Assist, 91 Circulation 2314-2318 (1995).

Even though cardiomyoplasty has demonstrated symptomatic improvement,studies suggest the procedure only minimally improves cardiacperformance. The procedure is highly invasive requiring harvesting apatient's muscle and an open chest approach (i.e., stemotomy) to accessthe heart. Furthermore, the procedure is expensive—especially thoseusing a paced muscle. Such procedures require costly pacemakers. Thecardiomyoplasty procedure is complicated. For example, it is difficultto adequately wrap the muscle around the heart with a satisfactory fit.Also, if adequate blood flow is not maintained to the wrapped muscle,the muscle may necrose. The muscle may stretch after wrapping reducingits constraining benefits and is generally not susceptible topost-operative adjustment. Finally, the muscle may fibrose and adhere tothe heart causing undesirable constraint on the contraction of the heartduring systole.

German Utility Model Patent Application DE 295 17 393 U1 describes apericardium prosthesis made from a biocompatible, non-expansiblematerial, or at least hardly expansible material which surrounds theheart. While the pericardium prosthesis prevents overexpansion of thewall of the heart, the action is deployed suddenly when the volume ofthe heart reaches the volume enclosed by the prosthesis. The suddendeployment may adversely affect the heart.

PCT application WO 98/58598 describes an elastic pouch for at leastpartially enveloping a heart. The elastic pouch always exerts the sameforce, substantially irrespective of its expansion, on the heart, sothat the heart is always relieved of substantially the same tensionirrespective of its volume. The volume of the pouch in the unexpandedstate is smaller than the volume of the heart at the stage of minimumfilling, thereby ensuring that the pouch is in contact with the heart inall stages of expansion. While such a force may help eject blood duringsystole, such a force could interfere with ventricle filling duringdiastole.

Commonly assigned U.S. Pat. No. 5,702,343 to Alferness dated Dec. 30,1997 (corresponding to PCT Published Application No. WO 98/14136)teaches a jacket to constrain cardiac expansion during diastole. Thepresent invention pertains to improvements to the invention disclosed inthe '343 patent.

SUMMARY OF THE INVENTION

According to a preferred embodiment of the present invention, a methodand device are disclosed for treating congestive heart disease andrelated cardiac complications such as valvular disorders. The inventionincludes a jacket of biologically compatible material. The jacketdefines an internal volume dimensioned for an apex of the heart to beinserted into the volume and for the jacket to be slipped over theheart. The jacket has a longitudinal dimension between upper and lowerends sufficient for the jacket to surround a lower portion of the heartpreferably between, or even including the valvular annulus of the heartand the ventricular lower extremities. The jacket is adjustable on theheart to snugly conform to an external geometry of the heart and assumea maximum adjusted volume for the jacket to constrain circumferentialexpansion of the heart beyond the maximum adjusted volume duringdiastole and to permit unimpeded contraction of the heart duringsystole.

The jacket is preferably constructed from a flexible material having amulti-axial expansion less than about 30% when said material is exposedto a load up to about 5 pounds per inch (9 Newtons per centimeter). Morepreferably, the expansion of the material along a first axis is betweenabout 30% and 40% when exposed to a uniaxial load between about 0.1pounds per inch (0.2 Newtons per centimeter) to about 0.5 pounds perinch (0.9 Newtons per centimeter) with no lateral constraint and theexpansion of the material along a second axis perpendicular to the firstaxis of said material is between about 20% and 30% when exposed to auniaxial load between about 0.1 pounds per inch (0.2 Newtons percentimeter) to about 0.5 pounds per inch (0.9 Newtons per centimeter)with no lateral constraint. Most preferably, the jacket material isoriented such a that the first axis (i.e., the more compliant direction)extends parallel to the longitudinal axis (AA-BB) of the heart.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a normal, healthy humanheart shown during systole;

FIG. 1A is the view of FIG. 1 showing the heart during diastole;

FIG. 1B is a view of a left ventricle of a healthy heart as viewed froma septum and showing a mitral valve;

FIG. 2 is a schematic cross-sectional view of a diseased human heartshown during systole;

FIG. 2A is the view of FIG. 2 showing the heart during diastole;

FIG. 2B is the view of FIG. 1B showing a diseased heart;

FIG. 3 is a perspective view of a first embodiment of a cardiacconstraint device according to the present invention;

FIG. 3A is a side elevation view of a diseased heart in diastole withthe device of FIG. 3 in place;

FIG. 4 is a perspective view of a second embodiment of a cardiacconstraint device according to the present invention;

FIG. 4A is a side elevation view of a diseased heart in diastole withthe device of FIG. 4 in place;

FIG. 5 is a cross-sectional view of a device of the present inventionoverlying a myocardium and with the material of the device gathered fora snug fit;

FIG. 6 is an enlarged view of a knit construction of the device of thepresent invention in a rest state;

FIG. 7 is a schematic view of the material of FIG. 6;

FIG. 8 shows a Force-Displacement plot of a material suitable for use inthe jacket of the invention;

FIG. 9 shows comparative Force-Displacement plots for material suitablefor use in the jacket of the invention, an elastic material and anon-elastic material;

FIG. 10 is a Force-Strain plot of material suitable for use in thejacket of the invention in which the load is exerted uniaxially, alongboth a first axis and second axis of the fabric and multiaxially;

FIG. 11 is a photograph of the material from FIG. 10. loaded along thesecond axis of the material at points AC, BC, CC and Dc;

FIG. 12 is a photograph of the material from FIG. 10 loaded along thefirst axis of the material at points A_(L), B_(L), C_(L) and D_(L);

FIG. 13 is a photograph of a variety of materials;

FIG. 14 is a Force-Strain plot of the uniaxial compliance for thematerials shown in FIG. 13′

FIG. 15 is a Force-Strain plot of the multiaxial compliance for thematerials shown in FIG. 13′

FIG. 16 is an illustrative Stress-Strain plot showing a linear elasticslope according to Hooke's Law;

FIG. 17 is an illustrative Stress-Strain plot showing the area ofresilience and the elastic limit of a material;

FIG. 18 is an illustration of a fiber in which the overlapping filamentsare substantially aligned with the fiber axis F-F;

FIG. 19 is an illustration of a fiber in which the overlapping filamentsare not substantially aligned with the fiber axis F-F;

FIG. 20 is an illustration of a fiber which is composed of continuousfilaments;

FIG. 21 is an example of a Force-Strain plot for a spherical shapedheart with multiaxial loading of material suitable for use in the jacketof the invention; and

FIG. 22 is an example of a Force-Strain plot for a cylindrical shapedheart with uniaxial loading of material suitable for use in the jacketof the invention.

DETAILED DESCRIPTION OF THE INVENTION

Congestive Heart Disease

With initial reference to FIGS. 1 and 1A, a normal, healthy human heartH′ is schematically shown in cross-section and will now be described inorder to facilitate an understanding of the present invention. In FIG.1, the heart H′ is shown during systole (i.e., high left ventricularpressure). In FIG. 1A, the heart H′ is shown during diastole (i.e., lowleft ventricular pressure).

The heart H′ is a muscle having an outer wall or myocardium MYO′ and aninternal wall or septum S′. The myocardium MYO′ and septum S′ definefour internal heart chambers including a right atrium RA′, a left atriumLA′, a right ventricle RV′ and a left ventricle LV′. The heart H′ has alength measured along a longitudinal axis AA′-BB′ from an upper end orbase B′ to a lower end or apex A′.

The right and left atria RA′, LA′ reside in an upper portion UP′ of theheart H′ adjacent the base B′. The right and left ventricles RV′, LV′reside in a lower portion LP′ of the heart H′ adjacent the apex A′. Theventricles RV′, LV′ terminate at ventricular lower extremities LE′adjacent the apex A′ and spaced therefrom by the thickness of themyocardium MYO′.

Due to the compound curves of the upper and lower portions UP′, LP′, theupper and lower portions UP′, LP′ meet at a circumferential groovecommonly referred to as the A-V groove AVG′. Extending away from theupper portion UP′ are a plurality of major blood vessels communicatingwith the chambers RA′, RV′, LA′, LV′. For ease of illustration, only thesuperior vena cava SVC′ and a left pulmonary vein LPV′ are shown asbeing representative.

The heart H′ contains valves to regulate blood flow between the chambersRA′, RV′, LA′, LV′ and between the chambers and the major vessels (e.g.,the superior vena cava SVC′ and a left pulmonary vein LPV′). For ease ofillustration, not all of such valves are shown. Instead, only thetricuspid valve TV′ between the right atrium RA′ and right ventricle RV′and the mitral valve MV′ between the left atrium LA′ and left ventricleLV′ are shown as being representative.

The valves are secured, in part, to the myocardium MYO′ in a region ofthe lower portion LP′ adjacent the A-V groove AVG′ and referred to asthe valvular annulus VA′. The valves TV′ and MV′ open and close throughthe beating cycle of the heart H′.

FIGS. 1 and 1A show a normal, healthy heart H′ during systole anddiastole, respectively. During systole (FIG. 1), the myocardium MYO′ iscontracting and the heart assumes a shape including a generally conicallower portion LP′. During diastole (FIG. 1A), the heart H′ is expandingand the conical shape of the lower portion LP′ bulges radially outwardly(relative to axis AA′-BB′).

The motion of the heart H′ and the variation in the shape of the heartH′ during contraction and expansion is complex. The amount of motionvaries considerably throughout the heart Ht, although the externaldimension of the heart H′ generally reduces from about 4% to about 10%from end diastole to end systole. The motion includes a component whichis parallel to the axis AA′-BB′ (conveniently referred to aslongitudinal expansion or contraction). The motion also includes acomponent perpendicular to the axis AA′-BB′ (conveniently referred to ascircumferential expansion or contraction).

Having described a healthy heart H′ during systole (FIG. 1) and diastole(FIG. 1A), comparison can now be made with a heart deformed bycongestive heart disease. Such a heart H is shown in systole in FIG. 2and in diastole in FIG. 2A. All elements of diseased heart H are labeledidentically with similar elements of healthy heart H′ except only forthe omission of the apostrophe in order to distinguish diseased heart Hfrom healthy heart H′.

Comparing FIGS. 1 and 2 (showing hearts H′ and H during systole), thelower portion LP of the diseased heart H has lost the tapered conicalshape of the lower portion LP′ of the healthy heart H′. Instead, thelower portion LP of the diseased heart H bulges outwardly between theapex A and the A-V groove AVG. So deformed, the diseased heart H duringsystole (FIG. 2) resembles the healthy heart H′ during diastole (FIG.1A). During diastole (FIG. 2A), the deformation is even more extreme.

As a diseased heart H enlarges from the representation of FIGS. 1 and 1Ato that of FIGS. 2 and 2A, the heart H becomes a progressivelyinefficient pump. Therefore, the heart H requires more energy to pumpthe same amount of blood. Continued progression of the disease resultsin the heart H being unable to supply adequate blood to the patient'sbody and the patient becomes symptomatic insufficiency. In contrast to ahealthy heart H′, the external dimension of the diseased heart Hgenerally reduces from about 4% to about 6% from end diastole to endsystole.

For ease of illustration, the progression of congestive heart diseasehas been illustrated and described with reference to a progressiveenlargement of the lower portion LP of the heart H. While suchenlargement of the lower portion LP is most common and troublesome,enlargement of the upper portion UP may also occur.

In addition to cardiac insufficiency, the enlargement of the heart H canlead to valvular disorders. As the circumference of the valvular annulusVA increases, the leaflets of the valves TV and MV may spread apart.After a certain amount of enlargement, the spreading may be so severethe leaflets cannot completely close (as illustrated by the mitral valveMV in FIG. 2A). Incomplete closure results in valvular regurgitationcontributing to an additional degradation in cardiac performance. Whilecircumferential enlargement of the valvular annulus VA may contribute tovalvular dysfunction as described, the separation of the valve leafletsis most commonly attributed to deformation of the geometry of the heartH. This is best described with reference to FIGS. 1B and 2B.

FIGS. 1B and 2B show a healthy and diseased heart, respectively, leftventricle LV′, LV during systole as viewed from the septum (not shown inFIGS. 1B and 2B). In a healthy heart H′, the leaflets MVL′ of the mitralvalve MV′ are urged closed by left ventricular pressure. The papillarymuscles PM′, PM are connected to the heart wall MYO′, MYO, near thelower ventricular extremities LE′, LE. The papillary muscles PM′, PMpull on the leaflets MVL′, MVL via connecting chordae tendineae CT, CT.Pull of the leaflets by the papillary muscles functions to prevent valveleakage in the normal heart by holding the valve leaflets in a closedposition during systole. In the significantly diseased heart H, theleaflets of the mitral valve may not close sufficiently to preventregurgitation of blood from the ventricle LV to the atrium duringsystole.

As shown in FIG. 1B, the geometry of the healthy heart H′ is such thatthe myocardium MYO′, papillary muscles PM′ and chordae tendineae CT′cooperate to permit the mitral valve MV′ to fully close. However, whenthe myocardium MYO bulges outwardly in the diseased heart H (FIG. 2B),the bulging results in displacement of the papillary muscles PM. Thisdisplacement acts to pull the leaflets MVL to a displaced position suchthat the mitral valve cannot fully close.

Having described the characteristics and problems of congestive heartdisease, the treatment method and apparatus of the present inventionwill now be described.

Jacket

In general, the device of the invention comprises a jacket configured tosurround the myocardium MYO. As used herein, “surround” means that thejacket provides reduced expansion of the heart wall during diastole byapplying constraining surfaces at least at diametrically opposingaspects of the heart. In some preferred embodiments disclosed herein,the diametrically opposed surfaces are interconnected, for example, by acontinuous material that can substantially encircle the external surfaceof the heart.

With reference now to FIGS. 3, 3A, 4 and 4A, the device of the presentinvention is shown as a jacket 10 of flexible, biologically compatiblematerial. As used herein, the term “biologically compatible material”refers to material that is biologically inert such that the materialdoes not adversely affect the surrounding tissue, for example, byeliciting excessive or injurious rejection responses, inflammation,infarction, necrosis, etc.

The jacket 10 is an enclosed material having upper and lower ends 12,14. The jacket 10, 10′ defines an internal volume 16, 16′ which iscompletely enclosed but for the open ends 12, 12′ and 14′. In theembodiment of FIG. 3, lower end 14 is closed. In the embodiment of FIG.4, lower end 14′ is open. In both embodiments, upper ends 12, 12′ areopen. Throughout this description, the embodiment of FIG. 3 will bediscussed. Elements in common between the embodiments of FIGS. 3 and 4are numbered identically with the addition of an apostrophe todistinguish the second embodiment and such elements need not beseparately discussed.

The jacket 10 is dimensioned with respect to a heart H to be treated.Specifically, the jacket 10 is sized for the heart H to be constrainedwithin the volume 16. The jacket 10 can be slipped around the heart H.The jacket 10 has a length L between the upper and lower ends 12, 14sufficient for the jacket 10 to constrain the lower portion LP. Theupper end 12 of the jacket 10 extends at least to the valvular annulusVA and further extends to the lower portion LP to constrain at least thelower ventricular extremities LE.

The volume 16 defined by the jacket 10 is preferably substantially thesame size as or larger than the volume of the heart H, in particular thelower portion LP of the heart, at the completion of systolic contractionsuch that the jacket 10 exerts no or only a slight pressure on the heartat end systole. Preferably, the pressure on the heart at end systole isno more than 10 mm Hg (1.3 kPa), more preferably no more than 5 mm Hg(0.66 kPa), most preferably no more than 2 mm Hg (0.27 kPa).

Generally, the jacket 10 is adjusted to a snug fit encompassing theexternal volume of the heart H during diastole such that the jacket 10constrains enlargement of the heart H during diastole withoutsignificantly assisting contraction during systole. The amount ofassistance during systole can be characterized by the pressure exertedby the jacket 10 on the heart H during systole. A jacket 10 that doesnot significantly assist contraction during systole will not exertsignificant pressure on the heart H at completion of systoliccontraction.

If the enlargement of the external dimension of the heart H isconsidered to be zero percent (0%) at completion of systole (endsystole) and one hundred percent (100%) at completion of diastole (enddiastole), the jacket 10 preferably exerts pressure between about 4 mmHg (0.53 kPa) and 40 mm Hg (5.3 kPa), more typically between about 4 mmHg (0.53 kPa) and 20 mm Hg (2.7 kPa) when the enlargement of theexternal dimension of the heart is between 50% and 100%. In contrast,when the enlargement of the external dimension of the heart H is below50%, it is preferred that the jacket 10 exert a pressure between about 2mmHg (0.27 kPa) and about 20 mmHg (2.7 kPa), preferably no more than 10mm Hg (1.3 kPa) on the heart H. It is noted that a jacket 10 that exertsa higher pressure (e.g., closer to 40 mm Hg (5.3 kPa)) at end diastoleis likely to exert a higher pressure (e.g., closer to 10 mm Hg (1.3kPa)) at end systole than a jacket that exerts a lower pressure (e.g.,closer to 5 mm Hg (0.66 kPa)) at end diastole.

Since enlargement of the lower portion LP is most troublesome, in apreferred embodiment, the jacket 10 may be sized so that the upper end12 can reside in the A-V groove AVG. Where it is desired to constrainenlargement of the upper portion UP, the jacket 10 may be extended tocover the upper portion UP.

Sizing the jacket 10 for the upper end 12 to terminate at the A-V grooveAVG is desirable for a number of reasons. First, the groove AVG is areadily identifiable anatomical feature to assist a surgeon in placingthe jacket 10. By placing the upper end 12 in the A-V groove AVG, thesurgeon is assured the jacket 10 will provide sufficient constraint atthe valvular annulus VA. The A-V groove AVG and the major vessels act asnatural stops for placement of the jacket 10 while assuring coverage ofthe valvular annulus VA. Using such features as natural stops isparticularly beneficial in minimally invasive surgeries where asurgeon's vision may be obscured or limited.

When the parietal pericardium is opened, the lower portion LP is free ofobstructions for applying the jacket 10 over the apex A. If, however,the parietal pericardium is intact, the diaphragmatic attachment to theparietal pericardium inhibits application of the jacket over the apex Aof the heart. In this situation, the jacket can be opened along a lineextending from the upper end 12′ to the lower end 14′ of jacket 10′. Thejacket can then be applied around the pericardial surface of the heartand the opposing edges of the opened line secured together after placedon the heart. Systems for securing the opposing edges are disclosed in,for example, U.S. Pat. No. 5,702,343, the entire disclosure of which isincorporated herein by reference. The lower end 14′ can then be securedto the diaphragm or associated tissues using, for example, sutures,staples, etc.

In the embodiment of FIGS. 3 and 3A, the lower end 14 is closed and thelength L is sized for the apex A of the heart H to be received withinthe lower end 14 when the upper end 12 is placed at the A-V groove AVG.In the embodiment of FIGS. 4 and 4A, the lower end 14‘is open and thelength L’ is sized for the apex A of the heart H to protrude beyond thelower end 14′ when the upper end 12′ is placed at the A-V groove AVG.The length L′ is sized so that the lower end 14′ extends beyond thelower ventricular extremities LE such that in both of jackets 10, 10′,the myocardium MYO surrounding the ventricles RV, LV is in directopposition to material of the jacket 10, 10′. Such placement isdesirable for the jacket 10, 10′ to present a constraint againstenlargement of the ventricular walls of the heart H.

After the jacket 10 is positioned on the heart H as described above, thejacket 10 is secured to the heart. Preferably, the jacket 10 is securedto the heart H through sutures. The jacket 10 is sutured to the heart Hat suture locations S circumferentially spaced along the upper end 12.While a surgeon may elect to add additional suture locations to preventshifting of the jacket 10 after placement, the number of such locationsS is preferably limited so that the jacket 10 does not restrictcontraction of the heart H during systole.

To permit the jacket 10 to be easily placed on the heart H, the volumeand shape of the jacket 10 are larger than the lower portion LP duringdiastole. So sized, the jacket 10 may be easily slipped around the heartH. Once placed, the jacket's volume and shape are adjusted for thejacket 10 to snugly conform to the external geometry of the heart Hduring diastole. Such sizing is easily accomplished due to theconstruction of the jacket 10. For example, excess material of thejacket 10 can be gathered and sutured S″ (FIG. 5) to reduce the volumeof the jacket 10 and conform the jacket 10 to the shape of the heart Hduring diastole. Such shape represents a maximum adjusted volume. Thejacket 10 constrains enlargement of the heart H beyond the maximumadjusted volume while preventing restricted contraction of the heart Hduring systole. As an alternative to gathering of FIG. 5, the jacket 10can be provided with other ways of adjusting volume. For example, asdisclosed in U.S. Pat. No. 5,702,343, the jacket can be provided with aslot. The edges of the slot can be drawn together to reduce the volumeof the jacket.

The volume of the jacket can be adjusted prior to, during, or afterapplication of the device to the heart. In one embodiment, the heart istreated with a therapeutic agent, such as a drug to decrease the size ofthe heart, prior to application of the jacket. In this embodiment, thetherapeutic agent acts to reduce the overall size of the heart prior tosurgery, and the jacket is thereafter applied to the reduced heart.Alternatively, the present invention can be used to reduce heart size atthe time of placement in addition to preventing further enlargement. Forexample, the device can be placed on the heart and sized snugly to urgethe heart to a reduced size. More preferably, the heart size can bereduced at the time of jacket placement through drugs, for exampledobutamine, dopamine or epinephrine or any other positive inotropicagents, or surgical procedure to reduce the heart size. The jacket ofthe present invention is then snugly placed on the reduced sized heartand constrains enlargement beyond the reduced size.

The jacket 10 is adjusted to a snug fit on the heart H during diastole.Care is taken to avoid tightening the jacket 10 too much such thatcardiac function is impaired. During diastole, the left ventricle LVfills with blood. If the jacket 10 is too tight, the left ventricle LVmay not adequately expand and left ventricular pressure will rise.During the fitting of the jacket 10, the surgeon can monitor leftventricular pressure. For example, a well-known technique for monitoringso-called pulmonary wedge pressure uses a catheter placed in thepulmonary artery. The wedge pressure provides an indication of fillingpressure in the left atrium LA and left ventricle LV. While minorincreases in pressure (e.g., 1 mm Hg (0.13 kPa) to 3 mm Hg (0.40 kPa)can be tolerated, the jacket 10 is snugly fit on the heart H but not sotight as to cause a significant increase in left ventricular pressureduring diastole.

Furthermore, because the wall of the right ventricle RV tends to bethinner than the wall of the left ventricle LV and the pressure in theright ventricle RV tends to be lower than the pressure in the leftventricle LV, the pressure exerted by the jacket 10 on the heart H ispreferably not greater than the end diastolic pressure of the rightventricle RV. If the pressure exerted by the jacket 10 is greater thanthe pressure of the right ventricle RV, expansion and/or filling of theright ventricle RV may be compromised. Generally, a jacket 10 thatimposes between about a 5% to about a 10% reduction in maximum diastolicvolume serves to reduce cardiac volume without compromising cardiacfunction. Generally, excessive pressure exerted by the jacket 10 on theheart H results in decreased cardiac output, increased central venouspressure, and/or decreased systolic pressure.

The jacket 10 can be used in early stages of congestive heart disease.For patients facing heart enlargement due to viral infection, the jacket10 permits constraint of the heart H for a sufficient time to permit theviral infection to pass. In addition to preventing further heartenlargement, the jacket 10 treats valvular disorders by constrainingcircumferential enlargement of the valvular annulus and deformation ofthe ventricular walls, causing displacement of the papillary muscles PMand chordae tendineae CT. Preventing displacement of these heartelements is important for allowing the leaflets MVL to fully close.

The fabric 18 of the jacket 10 is preferably tear and run resistant. Inthe event of a material defect or inadvertent tear, such a defect ortear is restricted from propagation by reason of the knit construction.

Material

Preferably the jacket 10 is constructed from a compliant, biocompatiblematerial. As used herein, the term “compliant” refers to a material thatcan expand in response to a force. “Compliance” refers to thedisplacement (in inches or centimeters) or strain (inches/inch or cm/cm)per a unit load (in pounds or kilograms) or load per unit width (inpounds per inch or kilograms per centimeter) for a material.“Elasticity” refers to the ability of the deformed material to return toits initial state after the deforming load is removed.

The compliance of the device is influenced by the fabric stitch andfabrication processing as well as interaction with the tissue afterimplantation. The multiaxial expansion of the material is generally lessthan about 30%, more typically less than about 25%, most typicallybetween about 10% and 20% as the material is exposed to a load up toabout 5 pounds per inch (9 N/cm) more typically between about 1 poundper inch (1.8 N/cm) and 3 pounds per inch (5 N/cm). As used herein, theterm “uniaxial expansion” refers to the expansion of a material alongonly one axis. The term “biaxial expansion” refers to the expansion of amaterial along a first axis and a second axis, typically the second axisis perpendicular to the first axis. The term “multiaxial expansion”refers expansion of a material along at least a first and a second axisand includes expansion along more than two axes.

The compliance of the material allows the jacket to be implanted withoutgaps and an insignificant load at end diastole. The compliance of thedevice along with the compliance of the heart allows the device toconform nicely to the irregular and unique shape of each heart.

FIG. 8 is a graph generated from data of a ball burst test using a 1.75inch diameter test area of sample material from the jacket of theinvention. The test was performed according to ASTM D3787-89. Accordingto this test, a ball is pressed against the center of the material witha measured force. As the load on the material is increased from 0 pounds(0 Newtons) to 36 pounds (160 Newtons), the material expandsmultiaxially. The initial part of the curve, up to about 5 pounds (22Newtons) and 0.30 in (0.76 cm) deformation, has a shallow (somewhathorizontal) slope. As the load is increased above 5 pounds (22 Newtons),the slope becomes more steep (i.e., more vertical). At a load of justover 36 pounds (160 Newtons), the fabric reaches its load capacity andfails.

The force exerted by the heart during diastolic filling is small, e.g.,less than 5 pounds (22 Newtons) of equivalent burst load. The normaldiastolic load is more typically equivalent to a 1 to 3 pound (4 to 13Newtons) ball burst load. Therefore, in use, the multiaxial expansion ofthe jacket 10 material remains within the shallow part of the curve. Atmaximum diastole, further expansion of the heart is resisted by theincreasing slope of the compliance curve.

FIG. 9 compares the compliance of the jacket of the invention with apouch constructed from a non-compliant material, such as described in DE295 17 393 (Hohmann), and a pouch constructed from an elastic material,such as described in PCT WO 98/58598 (Haindl).

Hohmann describes a pouch which is non-expansible. The pouch describedby Hohmann does not materially present a resisting force during diastolenor does the pouch materially provide an assisting force during systole.In FIG. 9, the Hohmann material is shown in an idealized form where thepouch has no force on the heart (“zero force region”) until maximumdiastolic filling, where the pouch does not expand (“expansion limit”).

Haindl describes a pouch that is smaller than the smallest volume of theheart and exerts a constant force on the heart which increases as theheart volume increases. As shown in FIG. 9, the material of Haindl has aprogressively increasing force on the heart (“elastic region”) untilmaximum diastolic filling, when the pouch becomes inelastic (“inelasticregion”) preventing further expansion.

In contrast to the pouch described by Hohmann, the material used in thejacket of the invention is compliant rather than elastic. In contrast tothe pouch described by Haindl, the jacket of the invention does notapply a significant or constant force on the heart H throughout thecardiac cycle. Instead, the jacket 10 of the invention generally appliesa greater pressure (e.g., about 6 mm Hg (0.8 kPa) to about 36 mm Hg (4.8kPa) more pressure) on the heart at end diastole than at end systole.

Compliance

Generally, the jacket 10 material is formed from intertwined fibers 20which are made up of a plurality of filaments 30 (See, e.g., FIGS. 6, 11and 12). The compliance of the material may be due to a variety offactors, including, but not limited to, the compliance of the individualfilaments 30 that make up the fibers 20, the relative movement of thefilaments 30 within a fiber 20, and/or the relative movement of theintertwined fibers 20 when subjected to load.

Additionally, the compliance of the material may be affected by theshape of the heart, the manner in which the jacket 10 is fitted on theheart H and tissue fibrosis. Fibrosis tends to reduce the acutecompliance of the material by preventing the openings of the fabric fromgeometrically changing shape.

The compliant nature of the jacket material can be easily contrastedwith elastomeric material. Whereas the compliant material of the jacketpreferably expands linearly up to about 30% to 50%, and elastically upto 70% without undergoing significant plastic deformation or failure,elastomeric material can be stretched repeatedly to at least twice itsoriginal length (200%), and upon release of the load, will returnwithout force to its approximate original length. Rubber and spandex areexamples of elastomeric materials. The force of the recoil depends uponthe density of the elastomeric fibers within the material.

Compliance due to the relative movement (e.g., geometric deformation ofthe fabric openings) of the intertwined fibers 20 may be affected by themanner in which the fibers 20 are entwined. For example, a knit materialwill tend to be more compliant than a woven material because the loopsof the knit are capable of deforming (e.g., widening or lengthening) toaccommodate applied stress. In comparison, woven materials tend to haveless elongation unless elastomeric fibers are used. Knit material alsotends to recover well from deformation because the loops attempt toreturn to their original positions. The looped configuration of thefibers accommodates this recovery more readily than does the interwovenconfiguration found in woven materials. The ease and quickness withwhich elastic recovery takes place is also dependent on the fibercomposition. The fibers 20 of the jacket 10 material may be entwined asa knit (for example, a warp knit) or as a weave. Preferably, the fibers20 of the jacket 10 material are entwined as a knit.

Compliance due to the relative movement of the intertwined fibers 20 canbe observed by the deformation of the structure of the fibers 20 withinthe material. Compliance can also be characterized using MTS Sintechtest equipment. At a given load, the strain refers to the percentageincrease in length of the fabric in that direction with the loadapplied. Preferably, the internal volume 16 of the jacket 10 is capableof multiaxial expansion up to about 30%, more typically between about10% and 20%, in response to a load or stress up to about 5 pounds perinch (9 N/cm) without significant plastic deformation or failure.

FIG. 10 is a plot showing the uniaxial compliance along a first axis andalong a second axis perpendicular to the first axis and the multiaxialcompliance of a material suitable for use in the jacket 10. Thecompliance parallel to the first axis of the fabric is slightly greaterthan the compliance perpendicular to the first axis (parallel to thesecond axis) of the fabric and the multiaxial compliance issignificantly lower than either uniaxial compliance. Preferably, thefirst axis (with slightly greater compliance) is oriented longitudinallyround the heart and the second axis (with slightly less compliance) isoriented circumferentially around the heart.

As shown in FIG. 10, between 20% and 40% strain, the slope of thecompliance curve for the multiaxial case is 3 to 4 times greater thaneither uniaxial compliance curve. However, between 70% and 100% strain,the extrapolated multiaxial compliance curve slope is only 1.3 to 1.4times greater than either uniaxial compliance curve. This indicates thatthe limiting stiffness of the fabric in multiaxial or uniaxial loadingis similar. However, strain to reach that constraint is dependent uponloading direction.

Compliance due to the relative movement of the intertwined fibers 20under uniaxial tension with no lateral constraint is depicted in FIGS.11 and 12. FIG. 12 shows a knit exposed to a load in the first uniaxialdirection, again with no lateral constraint (load is applied verticalwith reference to the photograph). FIG. 11 shows the same knit exposedto a load in a second uniaxial direction (perpendicular to the load inFIG. 12) with no lateral constraint (load is applied horizontal withreference to the photograph). A comparison of FIGS. 11 and 12 shows thatthe fabric compliance along one axis (vertical with reference to thephotograph) of the fabric is greater than the compliance perpendicularto that axis (horizontal with reference to the photograph). Preferably,the uniaxial compliance along a first axis (with no lateral constraint)is between about 30% and 40% when exposed to a load between about 0.1pounds per inch (0.2 N/cm) to about 0.5 pounds per inch (0.9 N/cm);between about 40% and 50% when exposed to a load between about 0.5pounds per inch (0.9 N/cm) to 1.0 pounds per inch (1.8 N/cm); andbetween about 50% and 60% when exposed to a load between about 1.0pounds per inch (1.8 N/cm) and 1.5 pounds per inch (2.6 N/cm).Preferably, the uniaxial strain along a second axis of the fabric(perpendicular to the first axis, with no lateral constraint) is about20% to about 30% when exposed to a load between about 0.1 pounds perinch (0.2 N/cm) to about 0.5 pounds per inch (0.9 N/cm); about 30% and40% when exposed to a load between about 0.5 pounds per inch (0.9 N/cm)to about 1.0 pounds per inch (1.8 N/cm); and between about 40% and 50%when exposed to a load between about 1.0 pounds per inch (1.8 N/cm) and1.5 pounds per inch (2.6 N/cm).

Four locations (A, B, C and D) are identified on both uniaxial curves inFIG. 10. These locations correspond approximately to the loads appliedto the fabric in the photos of FIGS. 11 and 12. For both uniaxialdirections, as the fabric load increases from A_(C) to D_(C) and fromA_(L) to D_(L) the compliance curve is fairly flat. The load ispredominantly accommodated by linearization of filament 30 and fiber 20crimp and geometric distortion of the knit pattern. The photos in FIGS.11 and 12 illustrate the distortion of the knit fabric as the openingsin the fabric collapse. For example, the looping configuration of a warpknit allows the openings to collapse more along a first axis (e.g.,along the warp direction) as compared to a second axis, perpendicular tothe first axis (e.g., along the weft direction). This is the reason forthe slightly greater compliance in the warp direction. Beyond pointsD_(C) and D_(L), the fabric becomes less compliant due to littleremaining geometric distortion. The compliance curves become linear andnearly parallel to each other beyond about 80% strain. The compliance inthis portion of each curve is primarily due to the elongation of thepoly(ethylene terephthalate) (e.g., polyester) filaments in the fibersafter the filament crimp has been removed.

As shown in FIG. 10, multiaxial loading of the fabric causes the fabricto be generally less compliant due to the inability of the fabric togeometrically deform. The multiaxial compliance of the jacket 10material up to 12% strain is essentially linear. The slight nonlinearportion of the curve is primarily due to yarn crimp and tightening ofthe loops that form the geometric structure. Beyond about 12% strain,the curve is linear and is controlled by the elongation of the filamentswithin the fiber. Generally, the slope of the compliance curve is 30% to40% less compliant than either of the uniaxial compliance curves.

Preferably, the knit is a so-called “Atlas knit” well known in thefabric industry. The Atlas knit is described in Paling, Warp KnittingTechnology, p. 111, Columbine Press (Publishers) Ltd., Buxton, GreatBritain (1970). The Atlas knit is a knit of fibers 20 having directionalexpansion properties. As shown in FIGS. 6, 11 and 12, the intertwinedfibers 20 include a plurality of longitudinally extending filaments 30,wherein opposing surfaces of said multi-filament fibers 20 define a cellstructure. The fibers 20 of the fabric 18 are woven into two sets offiber strands 21 a, 21 b having longitudinal axes X_(a) and X_(b). Thestrands 21 a, 21 b are interlaced to form the fabric 18 with strands 21a generally parallel and spaced apart and with strands 21 b generallyparallel and spaced apart.

For ease of illustration, fabric 18 is schematically shown in FIG. 7with the axis of the strands 21 a, 21 b only being shown. The strands 21a, 21 b are interlaced with the axes X_(a) and X_(b) defining adiamond-shaped open cell 23 having diagonal axes A_(m). In a preferredembodiment, the axes A_(m) are 5 mm in length when the fabric 18 is atrest and not stretched. The fabric 18 can stretch in response to aforce. For any given force, the fabric 18 stretches most when the forceis applied parallel to the diagonal axes A_(m). The fabric 18 stretchesleast when the force is applied parallel to the strand axes X_(a) andX_(b). The jacket 10 is constructed for the material of the knit to bedirectionally aligned for a diagonal axis A_(m) to be parallel to theheart's longitudinal axis AA-BB.

FIG. 6 illustrates the knit 18 in a rest state. FIGS. 11 and 12illustrate a knit exposed to a variety of loads in a first uniaxialdirection (FIG. 12), or a second uniaxial direction (FIG. 11),perpendicular to the first uniaxial direction. The directionalcompliance of the knit material is apparent from a comparison of FIG. 11and FIG. 12 (e.g., a load in one direction does not produce the samestrain as a load in the perpendicular direction).

FIG. 13 displays photographs of a variety of fabrics: (A) a knit fabric(thickness: 0.018 in.) suitable for use in the jacket of the invention;(B) a monofilament polypropylene mesh fabric (thickness: 0.026 in.),commercially available under the name Marlex (C. R. Bard, Inc., NewJersey); (C) a polyester mesh (thickness: 0.008 in.), commerciallyavailable under the name Lars Mesh (Meadox of Boston Scientific); (D) astretch polyester fabric (thickness: 0.027 in.), commercially availableas Meadox from Boston Scientific; and (E) a double velour material(thickness: 0.048 in.), commercially available under the name CooleyDouble Velour (Meadox of Boston Scientific). The results of uniaxial andmultiaxial compliance testing of these materials are shown in FIGS. 14and 15, respectively.

In FIG. 14, the Marlex, Lars and double velour are less compliant underuniaxial tension while the fabric with a uniaxial compliance mostsimilar to the material used in the jacket 10 of the invention is theMeadox stretch polyester. It is slightly more compliant than eitheruniaxial strains of the material used in the jacket 10 at low stress. Athigh stress, the stretch polyester has a compliance slope nearlyparallel and offset by about 5% to the right of the second axis uniaxialcurve of the fabric used in the jacket 10 of the invention.

The five fabrics were also tested under multiaxial loading and thecompliance is plotted in FIG. 15. Under multiaxial loading the Meadoxstretch polyester shows the greatest compliance. The slope of the curveat about 12% strain is nearly four times greater for the fabric used inthe jacket 10 of the invention than the slope for the stretch polyester.The multiaxial compliance of the other three commercial fabrics areagain much stiffer and nearly indistinguishable from one another. Theyall have compliance curves that are more than double the stiffness ofthe fabric used in the jacket 10 of the invention at low strain. None ofthe commercial fabrics tested provide desirable levels of compliance forboth uniaxial and multiaxial loading, yet provide the constrainingsupport required at higher strains to prevent continued heart dilationfor this application. Only the stretch polyester appears to havecompliance that is similar to the jacket 10 fabric, allowing conformanceto the heart. However, at larger strains the stretch polyester does notstiffen under multiaxial loads like the fabric used in the jacket 10,resulting in less constraining support.

The knit material has numerous advantages. Such a material is flexibleto permit unrestricted movement of the heart H (other than the desiredconstraint on circumferential expansion). The material is open defininga plurality of interstitial spaces for fluid permeability as well asminimizing the amount of surface area of direct contact between theheart H and the material of the jacket 10 (thereby minimizing areas ofirritation or abrasion) to minimize fibrosis and scar tissue.

The open areas of the knit construction also allows for electricalconnection between the heart and surrounding tissue for passage ofelectrical current to and from the heart. For example, although the knitmaterial is an electrical insulator, the open knit construction issufficiently electrically permeable to permit the use of trans-chestdefibrillation of the heart. Also, the open, flexible constructionpermits passage of electrical elements (e.g., pacer leads) through thejacket. Additionally, the open construction permits other procedures,e.g., coronary bypass, to be performed without removal of the jacket.

A large open area for cells 23 is desirable to minimize the amount ofsurface area of the heart H in contact with the material of the jacket10 (thereby reducing fibrosis). However, if the cell area 23 is toolarge, localized aneurysm can form. Also, a strand 21 a, 21 b can overlya coronary vessel with sufficient force to partially block the vessel. Asmaller cell size increases the number of strands thereby decreasing therestricting force per strand. In a preferred embodiment, the cell areaCA of cells in a particular row directly correlates with across-sectional circumferential dimension of the heart that the row ofcells surrounds relative to other cross-sectional circumferentialdimensions. That is, the greater the cross-sectional circumferentialdimension, the greater the area of the cells in the row of cellsdirectly overlying that cross-sectional circumferential dimension. By“correlating” cell area with cross-sectional circumferential dimensionof the heart, the cell area is determined as a function of thecross-sectional circumferential dimension of the heart. The cell area isdetermined so that when the weave material is applied to the heart or isshaped into a jacket and applied to the heart, each cell can widensufficiently to provide desirable cardiac constraint. Thus, the cellarea will be smaller for cells in a row applied over a region of theheart that has a smaller cross-sectional circumferential dimension thanthe cell area of cells in a row applied over a region of the hearthaving a larger cross-sectional circumferential dimension. Theappropriate maximum cell area may be, for example, 1 to 100 mm²,typically 16 to 85 mm². The maximum cell area is the area of a cell 23after the material of the jacket 10 is fully stretched and adjusted tothe maximum adjusted volume on the heart H as previously described.

Young's Modulus

Prior to discussing the contribution of filament elasticity and fiberstructure to the compliance of the jacket material, an overview ofYoung's Modulus will be provided.

Stress refers to the force (F) normalized by the cross sectional area(A) of an object. Stress can be represented by the following formula:F/A. For fabrics, unit load is commonly used in lieu of stress. The unitload is force (F) normalized by the width of a unit measure of fabric.Strain is defined as the change in length of the object normalized bythe initial length. Strain can be represented by the following formula:(1 ₁−1 ₀/1 ₀. Thus, if stress (or unit load) is plotted versus strain,the slope of the line in the elastic/linear range of the material givesthe elastic modulus or Young's modulus (E) of the object. (FIG. 16).

The stress-strain curve begins at zero stress and stops at the amount offorce which ruptures the fiber. The shape, length and height of astress-strain curve indicates how well a fiber resists elongation, howfar it will elongate before rupturing and how strong it is. The curvealso establishes the point at which a fiber will not recover fully froman applied stress.

According to Hooke's law, (at relatively low stress) the strain isproportional to stress and therefore the ratio of the two is a constantthat may be used to indicate the elasticity of the object. Young'sModulus may be loosely defined as the force required to elongate anobject. The elastic modulus can be calculated from measurements obtainedby pulling a sample of the object in a tensile testing machine. Young'sModulus for some polymers is provided in Table 1, below. TABLE 1 Young'sModulus for Some Polymers Modulus Material (Kpsi) Modulus (GPa)Polyimides 400-700 3-5 Polyesters 150-700 1-5 Nylon 300-600 2-4Polystryene 400-500   3-3.4 Polyethylene  30-100 0.2-0.7

The linear portion of the curve generally indicates the elastic behaviorof the material. Strains induced in the material due to a stress withinthe linear portion are totally recoverable once the stress is removed.The strain is thus referred to as elastic. When the initial linearsegment of the stress-strain curve rises steeply, a relatively largeincrease in stress produces a relatively small increase in strain (e.g.,the fiber has a high initial modulus). If the lines slopes at 45°, thenthere is a unit increase in strain for each unit increase in stress andthe initial modulus of the fiber is average. As the slope decreases orthe line become more horizontal, the initial modulus of the fiberbecomes lower. Fibers with low initial modulus are relatively easy toelongate. A slight force results in considerable fiber lengthening. Incontrast, a large force must be applied to fibers with high initialmodulus for small amounts of extension to occur.

In this initial segment of the stress-strain curve, the lengthening ofthe fiber is (1) the result of the degree to which polymers lying atangles to the fiber axis can be moved into alignment with the axis and(2) polymers with a nonlinear configuration can be straightened.Polymers that are spiraled and folded tend to act like springs; oncestress is released they attempt to return to their originalconfiguration. Thus, low modulus fibers tend to be less oriented thanhigh modulus fibers. Polymer slippage does not occur within the fiberduring the initial modulus segment of the stress strain curve.

As the stress on an object is increased, the plot of stress versusstrain becomes non-linear (FIG. 17). The elastic limit generally refersto the point where the curve begins to deviate from linearity. Beyondthe elastic limit, the material undergoes plastic deformation. Unlikeelastic deformation, plastic deformation is not recoverable, i.e., thechange is permanent. When a load is applied to an object and the objectdeforms and does not return to its original length when the load isremoved, the object is said to have undergone a plastic deformation. Atthe elastic limit, the polymers of the object begin to slip by oneanother as the stress becomes larger than the force of attractionbetween the polymers. However, when polymers are covalentlycross-linked, the crosslinks work to pull the polymers back theiroriginal positions.

Fibers

The compliance of the jacket 10 may also be affected by the relativemovement of the filaments 30 within the fibers 20. The relative movementof the filaments 30, in turn, may be affected by the structure of thefiber 20. A fiber 20 may be composed of overlapping filaments 30 thatare twisted about one another and held together by a binding mechanism(FIGS. 18 and 19) or the fiber 20 may be composed of continuousfilaments 30 (or a single filament) that extend longitudinally along thelength of the fiber 20 (FIG. 20), assembled with or without a twist. Thefiber 20 may be composed of filaments 30 that are substantially alignedwith the fiber axis F-F (FIG. 18) or the filaments 30 may lie moreobliquely with respect to the fiber 20 axis (FIG. 19).

Preferably, the fiber 20 is composed of continuous filaments 30. Becausecontinuous filaments 30 have less protruding ends, continuous filaments30 are less likely to abrade the surface of the heart H during systoleand diastole. In a fiber made of continuous filaments 30, thelengthening of the fiber 20 is generally the result of the degree towhich filaments 30 lying at angles to the fiber axis F-F can be movedinto alignment with the axis F-F and filaments 30 with a nonlinearconfiguration can be straightened. Filaments 30 that are spiraled andfolded tend to act like springs; once stress is released they attempt toreturn to their original configuration. Overlapping filaments 30 in afiber 20 may slip when exposed to stress, thus permanently altering or“stretching” the fiber 20.

Fibers 20 with multifilaments that are not substantially aligned arepreferred, such that fabric compliance from the fiber straightening canhelp to accommodate expansion of the ventricles during diastole.Generally, preferred fibers include 70 Denier textured polyester.

Filaments

The elasticity of the filaments 30 which make up the fibers 20 may alsoaffect the compliance of the jacket 10. The filaments 30 are preferablyformed of a non-elastomeric material (i.e., the filament 30 does notreturn to its approximate original length with force), preferably thefilament is constructed from a material with a moderate modulus ofelasticity, more preferably between 1.0 GPa (150 Kpsi) and 5 GPa (700Kpsi). In a preferred embodiment, the filaments 30 include 34 strands toconstruct the 70 Denier poly(ethylene terephthalate) (e.g., polyester)fibers 20. While poly(ethylene terephthalate) is presently preferred,other suitable materials may include polytetrafluoroethylene (PTFE),expanded PTFE (ePTFE), polypropylene, titanium and stainless steel.

With the foregoing, a device and method have been taught to treatcardiac disease. The jacket 10 constrains further undesirablecircumferential enlargement of the heart while not impeding other motionof the heart H. With the benefits of the present teachings, numerousmodifications are possible. For example, the jacket 10 need not bedirectly applied to the epicardium (i.e., outer surface of themyocardium) but could be placed over the parietal pericardium. Further,an anti-fibrosis lining (such as a PTFE coating on the fibers of theknit) could be placed between the heart H and the jacket 10.Alternatively, the fibers 20 can be coated with PTFE.

The jacket 10 is low-cost, easy to place and secure, and is convenientfor use in minimally invasive procedures. The thin, flexible fabric 18permits the jacket 10 to be collapsed and passed through a smalldiameter tube in a minimally invasive procedure.

The jacket 10, including the knit construction, freely permitslongitudinal and circumferential contraction of the heart H (necessaryfor heart function). Unlike a solid wrap (such as a muscle wrap in acardiomyoplasty procedure), the fabric 18 does not impede cardiaccontraction. After fitting, the jacket 10 is inelastic to preventfurther heart enlargement while permitting unrestricted inward movementof the ventricular walls. Because the jacket 10 is not constructed froman elastomeric material, it does not substantially assist the heartduring systolic contraction.

The open cell structure permits access to coronary vessels for bypassprocedures subsequent to placement of the jacket 10. Also, incardiomyoplasty, the latissimus dorsi muscle has a variable and largethickness (ranging from about 1 mm to 1 cm). The material of the jacket10 is uniformly thin (less than 1 mm thick). The thin wall constructionis less susceptible to fibrosis and minimizes interference with cardiaccontractile function.

Animal test studies on the device show the efficacy of the invention.Test animals were provided with the device 10 of FIG. 3. The animals'hearts were rapidly paced to induce enlargement. After six weeks,animals without the device experienced significant heart enlargementwhile those with the device experienced no significant enlargement.Further, animals with the device had significantly reduced mitral valveregurgitation.

In addition to the foregoing, the present invention can be used toreduce heart size at the time of placement in addition to preventingfurther enlargement. For example, the device can be placed on the heartand sized snugly to urge the heart to a reduced size. More preferably,the heart size can be reduced at the time of jacket placement throughdrugs (e.g., dobutamine, dopamine or epinephrine or any other positiveinotropic agents) to reduce the heart size. The jacket of the presentinvention is then snugly placed on the reduced sized heart and preventsenlargement beyond the reduced size.

From the foregoing, a low cost, reduced risk method and device aretaught to treat cardiac disease. The invention is adapted for use withboth early and later stage congestive heart disease patients. Theinvention reduces the enlargement rate of the heart as well as reducingcardiac valve regurgitation.

EXAMPLES OF IMPLANT SCENARIOS Example 1

In this example, the heart is assumed to be spherical in shape and 46 cm(18 in.) in diameter at end diastole. The device is installed around theheart and adjusted to create a uniform loading of the fabric. Becausethe heart is spherical in shape, the pressure is uniformly applied tothe heart and resisted by the device like a spherical pressure vessel,where the load per unit width is pd/4 (Note: p=pressure, d=diameter).Since the load is uniform the multiaxial compliance curve of the fabricwould be most applicable. FIG. 21 illustrates the installed conditionfor an end diastolic device pressure of 20 mm Hg (2.7 kPa). Thiscorresponds to 0.6 lbs/in. fabric load for this size heart.

During systole the heart muscle contracts and the external dimension isreduced. On average, the heart reduces circumferentially byapproximately 6% and longitudinally by 4% from end diastole to endsystole. Thus, for the case of a 4% to 5% change in circumference anddiameter is assumed. This linear dimensional change relates to a 12% to15% external ventricular volume change for a spherical heart. At endsystole, FIG. 21 shows that the circumference reduces to 44 cm (17.3in.) and the applied pressure drops from 20 mm Hg (2.7 kPa) to 4 mm Hg(0.53 kPa). For this condition the fabric load is only 0.1 lbs/in andthe device is nearly unloaded.

The pressure applied by the device is helping to offload heart wallstress throughout the cardiac cycle. This support is greatest at enddiastole when the heart volume is greatest (relaxing between systoliccontractions). Although the diastolic phase is considered relaxing, themyocardium may never actually completely relax. Some slight loadingduring diastole may not significantly restrict filling but rather serveto off load the wall stress throughout the cardiac cycle.

If the heart becomes improved and reduces in size, the device willbecome unloaded at end systole. Only a 16% volume reduction will resultin the device being completely unloaded. If the heart continues todilate due to continued disease progression, load support from thejacket increases dramatically. With less than 4% increase dilation, theapplied pressure would double to a load of 40 mm Hg (5.3 kPa). Thebiaxial compliance curve of the fabric results in very significantpressure changes for relatively small volume changes.

Example 2

In this example, the heart is assumed to be cylindrical in shape andagain 46 cm (18 in.) in circumference at end diastole. The device isinstalled around the heart and adjusted to create a primarilycircumferential loading of the fabric with the end effects andlongitudinal loading assumed to be negligible. Because the heart iscylindrical in shape, the circumferential load per unit width is pd/2.Note that based on the pressure vessel theory, this is twice the loadresisted in the spherical shape of Example 1 for the same pressure.Since the load is only circumferential, the uniaxial compliance curve ofthe fabric would be most applicable. FIG. 22 illustrates the installedcondition for an end diastolic device pressure of 10 mm Hg (1.3 kPa).This corresponds to 0.6 pounds per inch (1.1 N/cm) fabric load for thissize heart.

Similar to Example 1, during systole the heart muscle contracts and theexternal dimensions of the heart are reduced. If a 6% change incircumference and diameter is assumed, along with a 4% longitudinallength change, the external ventricular volume change would beapproximately 17%. At end systole, FIG. 22 shows that the circumferencereduces to 44 cm (17.3 in.) and the applied pressure only drops from 10mm Hg (1.3 kPa) to 8 mm Hg (1.1 kPa). For this condition, the fabricload is nearly unchanged from 0.6 to 0.5 pounds per inch (1.1 N/cm to0.88 N/cm). This small load change is due to a flat compliance curve.

Similar to Example 1, the pressure applied by the device is helping tooffload heart wall stress throughout the cardiac cycle. However, in thiscase the support from the jacket is nearly constant throughout thecardiac cycle.

For the case shown in FIG. 22, if the heart becomes improved and reducesin size, the device will continue to be supported for a volume reductionof up to 70%. This compliance/load scenario would result in longer termsupport than in Example 1. As the heart diameter reduces and progressesto the left on the compliance curve, the loading is gradually lowered.This will continue until a very significant 70% external volumereduction occurs. If the heart continues to dilate due to continueddisease progression or exercise overload, the load support from thejacket increases dramatically with a significant increase in dilation. A30-mm Hg (4 kPa) increase in pressure to the 40 mm Hg (5.3 kPa) designload will allow a 30% increase diametrical dilation. The uniaxialcompliance curve of the fabric allows very large changes in size withrelative small load changes, assuming the load remains unidirectional.

The therapy provided by the device may be a combination of Examples 1and 2. When installed the jacked behaves as in Example 1 if it isadjusted to provide a nearly uniform load. Then as the heart improvesand reduces in size, the loading may become more unidirectional ifeither the longitudinal or circumferential directions do not change atthe same rate. This would change the compliance curve to behave morelike Example 2. The actual fabric compliance curve may transition frommultiaxial to uniaxial as the heart shape changes.

1-12. (canceled)
 13. A device for treating a disease of a heart, thedevice comprising: a jacket of flexible material formed with a base endand an apex end and having an interior, said base end sized to be placedover an apex of said heart and moved toward a base of said heart for atleast a portion of said heart to be received within said interior; saidmaterial compliant for said jacket to conform to an external geometry ofsaid portion of said heart; said material adapted for said jacket toexert a maximum pressure on said heart less than 40 mm Hg.
 14. A deviceaccording to claim 13 wherein said maximum pressure is a pressure onsaid heart at end diastole.
 15. A device according to claim 13 whereinsaid maximum pressure is less than 20 mm Hg.
 16. A device according toclaim 15 wherein said maximum pressure is a pressure on said heart atend diastole.
 17. A device according to claim 13 wherein said materialis adapted for said jacket to exert a range of pressure on said heart of2 mm Hg to 40 mm Hg.
 18. A device according to claim 13 wherein saidjacket is sized for said interior of said jacket to be smaller than anexternal geometry of said heart prior to application of said device. 19.A device according to claim 13 wherein said material has a compliancefor said jacket to conform with an external shape of said portion ofsaid heart without application of forces on said heart which wouldotherwise impair cardiac function.
 20. A device according to claim 13wherein said jacket is open at said apex end.
 21. A device according toclaim 13 wherein said jacket is closed at said apex end.
 22. A deviceaccording to claim 13 wherein said material constructed of a pluralityof flexible elongated members interconnected to form a jacket material.23. A device according to claim 22 wherein said elongated members arefibers formed of multiple filaments.
 24. A device according to claim 22wherein said elongated members have a plurality of bends whichstraighten for said jacket to expand.
 25. A device according to claim 22wherein said elongated members are metal.
 26. A device according toclaim 25 wherein said metal is stainless steel.
 27. A device accordingto claim 25 wherein said metal is titanium.
 28. A device according toclaim 22 wherein said elongated members are coated.
 29. The deviceaccording to claim 13 wherein said jacket is adapted to constrain saidheart from expanding beyond a maximum volume.
 30. The device accordingto claim 13 wherein said jacket is collapsible for placement through aminimally invasive surgical instrument.
 31. A method for treating adisease of a heart, the method comprising: a. selecting a deviceincluding: i. a jacket of flexible material formed with a base end andan apex end and having an interior, said base end sized to be placedover an apex of said heart and moved toward a base of said heart for atleast a portion of said heart to be received within said interior; ii.said material compliant for said jacket to conform to an externalgeometry of said portion of said heart; iii. said material adapted forsaid jacket to exert a maximum pressure on said heart less than 40 mmHg. b. placing said jacket on said heart with said material surroundingat least the ventricles of said heart with said jacket exerting no morethan said maximum pressure.
 32. A method according to claim 31 whereinsaid step of placing a jacket includes covering a lower end of saidheart.
 33. A method according to claim 31 wherein said step of placingsaid jacket includes leaving a lower end of said heart exposed.
 34. Amethod according to claim 31 wherein said maximum pressure is a pressureon said heart at end diastole.
 35. A method according to claim 31wherein said maximum pressure is less than 20 mm Hg.
 36. A methodaccording to claim 35 wherein said maximum pressure is a pressure onsaid heart at end diastole.
 37. A method according to claim 31 whereinsaid placing includes placing said jacket on said heart for said jacketto exert a range of pressure on said heart of 2 mm Hg to 40 mm Hg.
 38. Amethod according to claim 31 including sizing said jacket for saidinterior of said jacket to be smaller than an external geometry of saidheart prior to application of said device.
 39. A method according toclaim 31 wherein said material has a compliance for said jacket toconform with an external shape of said portion of said heart withoutapplication of forces on said heart which would otherwise impair cardiacfunction.
 40. A method according to claim 31 wherein said materialconstructed of a plurality of flexible elongated members interconnectedto form a jacket material.
 41. A method according to claim 40 whereinsaid elongated members are fibers formed of multiple filaments.
 42. Amethod according to claim 40 wherein said elongated members have aplurality of bends which straighten for said jacket to expand.
 43. Amethod according to claim 40 wherein said elongated members are metal.44. A method according to claim 43 wherein said metal is stainlesssteel.
 45. A method according to claim 43 wherein said metal istitanium.
 46. A method according to claim 40 wherein said elongatedmembers are coated.
 47. The method according to claim 31 wherein saidplacing includes placing said jacket on said heart for said jacket toconstrain said heart from expanding beyond a maximum volume.
 48. Amethod according to claim 31 wherein said jacket is delivered minimallyinvasively to said heart by collapsing said jacket into a hollowminimally invasive surgical tool.